1. Field of the Invention
The Related Physical Law and Different Ways to Make Use of It
The term "evaporative cooling devices" denominates several disparate systems and apparatuses, all of which function in diverse ways to take advantage of one and the same law of physics. Under that law a change of a liquid phase (for instance, water) into vapor phase can produce reduction of temperature with certain quantum of heat energy (called "heat of vaporization") involved in that phase change. This reduction of temperature is a common phenomenon and it is also observable in Nature. For instance, a sudden rain on a hot summer day will cause a drop in air temperature, because the evaporating rain removed the heat energy (i.e. the heat of vaporization) from the air.
This temperature drop resulting from a change of phases is a desired situation in operation of evaporative coolers. Raw water is introduced into an evaporative cooler for its vaporization with heat energy extracted from the outdoor air of a convenient quality. When a portion of water evaporates and the air drops its temperature, some water vapors are absorbed by the outdoor air passing through the heat exchange medium. By complete evaporation a volume of 1 lb of water produces a cooling effect of approximately 1050 Btu. The cooled air is a desired product of exchange of heat energy and is directed to rooms where cooling is desired. The water, which is an active agent of cooling, after completed heat exchange becomes useless and it is discharged to a drain.
This described arrangement is not the only one where Man makes use of that underlying physical law. An entirely different concept of cooling by evaporating water takes place in "cooling towers". Those are rather larger constructions to cool down hot water, not hot air, as is practiced in "evaporative coolers". There are "direct" and "indirect" types of cooling towers. One design of "indirect" type of cooling tower is described in U.S. Pat. No. 3,820,353 granted on Jun. 28, 1974 to Shiraishi et al. for "Evaporative cooling apparatus".
However, a more common one is the type of "cooling tower" in which hot water is brought for its subsequent cooling by direct exposure to outdoor air. One such representative design of "direct" type "cooling tower" is described in U.S. Pat. No. 3,627,032 to Glad et al for a "Cooling tower water treatment system". In "cooling towers", unlike in "evaporative coolers", the subject of the cooling process is hot water, and cooled water (not cooled air) is the end product of cooling. In Glad's, and similar types of "cooling towers", hot water is cascading over vertical surfaces, or is sprayed against a draft of outdoor air. In a direct contact with ambient air hot water releases its heat energy to passing air. Hot and humid air, after the contact with hot water, is discharged to atmosphere as useless substance, while cooled water is collected in the basin of the "cooling tower" from where it is recirculated back for its further use.
It can be seen that "evaporative coolers" differ from "cooling towers" in design as well as in operation, and in nature of their end products.
2. Description of the Prior Art
Explanation of some basic terms used hereinafter:
Evaporative cooling--a process in which hot air is in direct contact with water causing water to evaporate. During this process sensible heat is removed from the air (i.e. the air cools down).
Evaporative coolers--smaller mechanical devices used for cooling rooms and premises. In "evaporative coolers", ambient air is drawn through heat exchange media wetted with process water to release a portion of its heat energy while absorbing some moisture. Evaporative coolers reduce the heat load in rooms or premises by forcing out hot indoor air by the cooled outdoor air, providing acceptable comfort level to inhabitants. Evaporative coolers exist as "direct" or "indirect" type; direct type prevails.
Heat exchange media--porous stationary or rotary pads wetted with circulating water. Through them the hot outside air is drawn for removing its heat energy.
Scalants--water hardness minerals dissolved in the raw process water and deposited on heat exchange media after the water evaporates.
Raw water--potable water generally containing scalants, supplied to an evaporative cooler from city wells and reservoirs or other natural water resources.
Circulating process water--a mixture of raw water and excess process water (cascading over the heat exchange media and enriched by scalants washed down from these media), collected in the water basin of an evaporative cooler.
Evaporative coolers have been and are still being manufactured. The manufacturer's instructions for operating such evaporating coolers, such as set forth in the "use and care" manuals enclosed with the evaporative coolers, require the use of a "bleed-off" system by which a portion of the circulating process water is eliminated from the evaporative cooler. The same "use and care" manual also recommends against use of chemical additives or any water treatment other than bleed-off in operating the cooler.